74 Hereditanj Lcftliandednean 



of the lefthandedness "determiner," and the general agreement with 

 Mendelian hiws of inheritance. 



Charts Figs. 63 to G7 present striking histories from the foregoing 

 group. In the first four the ancestors to, and including, the grand- 

 parents (Fig. 64 ; also gi-eat-gi'undparents) are said to have been normal. 

 The immediate parents may be presumed to be in the simplex condition 

 (heterozygous dominants). These four pedigrees show unmistakeably that 

 lefthandedness is due to a positive factor (presence of a "determiner"). 

 The reported incidence of lefthandedness in the several fraternities 

 defies reconciliation with strict Mendelian principles'. Similarly, 

 pedigree Fig. 67. Here the entire childship of a double lefthanded 

 mating is reported ntiniuil. This liistory, as also many other facts, show 

 that righthandedness also depends upon a positive factor. Chai'ts 63 

 and 67 are directly contradictory, not only with i-eference to each other, 

 but also as concerns numerous other pedigrees and the princijjles of 

 lefthanded inheritance (Mendelian) deduced from them. These will be 

 iinther discussed among exceptions considered below. 



Ciiart Fig. 68 is from the parent-child group. It is especially 

 interesting in fulfilling the Mendelian expectation of a DR x KR, the 

 probable cross. 



Chai'ts Figs. 69 to 74 ai'e tlie most important and most extensive 

 among the "collateral" group noted above. Concerning the lefthanded 

 male parent of 71 it is rect)rded that he "bats leftlianded in base-ball." 

 The fraternities of Figs. 69 and 74 give the Mendelian ratio ioi' the 

 most probable crosses involved, namely DR x DR, and the remaindi'r 

 are not seriously at variance with exjDectanc}' in view of the pi-obable 

 ancestry. 



Chart, Fig. 7"), was contributed by Professor F. A. Hodge, Winthrop 

 College, S.C. ; and Fig. 76 by Mr Frank J. Sconce, of Fairview, Illinois 

 (filed at the Eugenics Record Oftice, Cold Spring Harbor, Long Island). 

 Botli histories demonstrate the recessive nature of decided lefthanded 

 bias, and leave no doubt regarding the general valency of Mendelian 

 laws in hereditary lefthandedness. Chart Fig. 77 (Prof. Hodge) appears 

 to countervail this deduction ; but the reported lefthanded parents have 

 but a mild bias, as I have learned from subsequent inquiry, since " they 

 write with the right hand, and do only certain things with the left 

 hand." Complete recession, under the circumstances, would hardly be 

 expected. This pedigi-ee was charted as Fig. 32 of my " Studies in 

 Human Heredity." 



' The possibility is suggested that lefthandedness (and ambidexterity) may be degrees 

 of the same condition due to an "inhibitor" to righthandedness. 



